Gas-blast circuit breaker with noise-reducing exhaust muffler assembly

ABSTRACT

A noise-reducing exhaust muffler for a gas-blast circuit breaker comprises spaced end walls and four concentric tubular members mounted between the end walls. Exhaust gases enter through one end wall, flow into the space enclosed by the first tubular member, then flow radially outward through holes in the first, second, and third tubular members, and then axially of the muffler between the third and fourth tubular members. The holes in the third and second tubular members are in axially staggered locations so as to introduce additional turns into the flow path and provide solid wall barriers to the radiation of sound energy.

United States Patent inventors Francis Kirschner East Hills, N.Y.; Vincent N. Stewart, Springfield; Ugo R. f Tognella, Philadelphia, Pa. App]. No. 6,244 Filed Jan. 27, 1970 Patented Nov. 2, 1971 Assignee General Electric Company GAS- BLAST CIRC UIT BREAKER WITH NOISE- REDUCING EXHAUST MUFFLER ASSEMBLY 11 Claims, 4 Drawing Figs.

US. Cl. zoo/14s, 200/150 0 Int. c|..... H01h aa/ss Field oiSelrch ZOO/148.3, 150 a, 148

References Cited UNITED STATES PATENTS 1,045,419 11/1912 Matula 200/150H 1,680,671 3/1928 Eschholz 200/150 H 2,302,592 11/1942 Amer 200/148 C 3,134,876 5/1964 Chang et al ZOO/148C FOREIGN PATENTS 622,970 12/1935 Germany 200/150 H Primary Examiner-Robert S. Macon Attorneys-J. Wesley Haubner, William Freedman, Frank L.

Neuhauser, Oscar B. Waddell and Joseph B. Forman PAIENTEDNBV 2 m "SHEET 10F 2 Y //vv/v TORS I VINCENT /V. STEWART, UGO R. 7bGA/ELLA, fkA/vc/s Amsc/m/m, 6y ATTORNEY GAS-BLAST CIRCUIT BREAKER WITH NOISE- REDUCING EXHAUST MUFFLER ASSEMBLY This invention relates to a gas-blast type of electric circuit breaker and, more particularly, relates to a muffler assembly for reducing the noises resulting from the flow of hot exhaust gases from the circuit breaker to the surrounding atmosphere.

In a gas-blast type of circuit breaker, circuit interruption is effected by causing a high-speed blast of pressurized gas to flow for a short period through the usual arching region of the circuit breaker. This blast facilitates circuit interruption by cooling the arc and by cleansing the arching region of hot metallic vapors and other highly heated arcing products. Upon leaving the arcing region, the highly heated gases are discharged to the surrounding atmosphere in a short and intense burst. In most prior gas-blast circuit breakers, the heated gases are then flowing at high speed, and the result is a loud noise, which in many cases is objectionable.

For reducing the amount of noiseresulting from circuitbreaker operation, it has been proposed that the circuit breaker be provided with a noise-reducing muffler through which the exhaust gases pass before entering the atmosphere. An example of such a muffler is that shown in U.S. Pat No. 3,134,876 Chang et al. assigned to theflassignee of the present invention. While the muffler of that patent does substantially reduce the amount of noise resulting from circuit-breaker operation, in certain applications it is necessary to achieve still greater reductions.

An object of our invention is to provide a muffler that is capable of producing the desired greater reductions in noise level and which, at the same time, is highly compact and does not create an objectionable amount of back pressure that could impair the ability of the circuit breaker to perform its intended arc-extinguishing function.

Another object is to provide a compact and relatively inexpensive mnffler in which there are no straight line paths leading from the inner chambers of the muffler to the exterior that are not intercepted by solid wall portions of the muffler.

Another object is to provide a muffler in which most of the noise entering the muffler or developed insidethe muffler can reach a point remote from the circuit breaker only after having passed through two solid wall portions or through a tortuous path.

In carrying out the invention in one form, we provide a muffler comprising a pair of spaced-apart end walls and a first tubular member extending axially of the muffler between said end walls to define a diffuser chamberinternally thereof. The first tubular member has radially extending perforations at spaced-apart locations about a major portion of its length and periphery for allowing exhaust gases to flow radially outward therethrough. In one end wall, there is an inlet to the diffuser chamber for directing exhaust gases axially of the muffler toward the other end wall. A generally conical deflector on the other end wall has a base surrounded by the first tubular member and a vertex projecting from the base toward said one end wall. A perforated second tubulajr member surrounding and spaced from the first tubularrne'mber defines the outer perimeter of an expansion chamber between the first and second tubular members. A perforated third tubular member surrounding and spaced from the second defines the outer perimeter of a reentry chamber between the second and third tubular members. The second tubular member has far more perforations in its end regions than in its longitudinally central region, while the third tubular member has its perforations located predominantly in its longitudinally central region. A fourth tubular member surrounds the third in spaced relation and forms the outer periphery another expansion chamber substantially filled with compacted porous material. The fourth tubular member is substantially imperforate but exhaust openings are provided at opposite ends of the muffler through which exhaust gases vent after flowing axially of the muffler through said compacted porous material.

For better understanding of the invention, reference may be had to the following description taken in connection with the accompanying drawing, wherein:

FIG. 1 is a side elevational view of a portion of an electric circuit breaker embodying one form of the invention.

FIG. 2 is a plan view of the circuit breaker of FIG. 1 with a portion shown in section taken along the line 2-2 of FIG. 1.

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 1 and illustrating an exhaust mufiler embodying one form of our invention.

FIG. 4 is an enlarged partial sectional view showing a modification using screening for retaining diffuser material at the outer ends of the exhaust muffler.

Referring now to the drawings and particularly to FIGS. 1 and'2, the circuit breaker shown therein comprises a metal tank 10 mounted upon an insulating column 11 and an exhaust mufiler assembly 9 of the present invention mounted at one side of the tank. The tank is at a high voltage with respect to ground, and the insulating column 11 serves to electrically isolate the tank from ground as well as to support it. Tank I0 is normally filled with pressurized air that serves as an arc-extinguishing medium, as will be described hereinafter. The basic circuit breaker structure within the tank generally corresponds to that disclosed in detail and claimed in U.S. Pat. No. 2,783,338-Beatty, assigned to the assignee of the present invention. The structure of the circuit breaker will be described herein only to the extent believed necessary to convey an understanding of the present invention that relates to the exhaust muffler assembly. Reference may be had to the Beatty patent if a more detailed description is desired of the circuit breaker.

Referring now to FIG. 2 the structure within the tank 10 comprises two pairs of relatively movable contacts. One pair of contacts comprises a stationary contact 12 and a movable contact 14. The other pair of contacts comprises a stationary contact 13 and a movable contact 15. The movable contacts 14 and 15 are mounted on two stationary pivots 16 and I7 carried by a central metallic support 20 that is mechanically and electrically connected to the tank 10. The stationary contact 12 is shown mounted on the inner end of a lead-in bushing 25 projecting into the tank through its left-hand end wall and providing an electrical connection through a conductive stud 27 between the stationary contact 12 and a terminal 29 of the circuit breaker. The other stationary contact 13 is shown mounted on a bushing 26 projecting into the tank through its right-hand end wall and providing a connection through a conductive stud 28 between the other terminal 30 of the circuit breaker and the contact 13. The lead-in bushings 2 5 and 26 insulate the contacts 12 and 13 from the tank 10 when the circuit breaker is open.

For imparting opening or closing motion to the movable contacts 14 and 15, a common driving member in the form of a reciprocal crosshead 35 is provided. The movable contact 14 is coupled to this crosshead 35 by means of a link 36 pivotally connected at its respective opposite ends to the crosshead 35 and the movable contact 14, whereas the movable contact 15 is coupled to the crosshead 3 5 by means of a second link 37 pivotally connected at its respective opposite ends to the crosshead 35 and the movable contact I5. As viewed in FIG. 2, upward movement of the crosshead 35 causes the lower ends of the movable contacts 14 and I5 to separate from their respective stationary contacts 12 and I3, and move into an open position; whereas return movement of the crosshead 35 returns the movable contacts 14 and 15 from the open position to a closed position.

For controlling the motion of the crosshead 35 so as to effect opening and closing of the movable contacts in this manner, a pneumatic-operating mechanism is provided within the central metallic support 20. The details of this operating mechanism form no part of the present invention and therefore will not be described in this application. Preferably, how ever, the operating mechanism is of the type disclosed and claimed in the aforementioned Beatty patent U.S. Pat. No. 2,783,338.

For extinguishing the arcs formed between the contacts upon opening .of the circuit breaker, a blast of pressurized air is caused to flow through the arcing region. This blast of air is controlled by a normally closed blast valve 38 mounted within the metallic support 20. When the blast valve 38 is lifted into its open position, communication is established between an exhaust passage 40 and the space within the tank through exhaust orifices 39. This causes pressurized gas within the tank to flow through the arcing region into the exhaust passage 40 via paths generally indicated by the dotted line arrows 41 of FIG. 2. When circuit interruption is completed, the blast valve is returned to its closed position to terminate the gas blast. The blast valve and its control means are described in greater detail in the aforementioned Beatty patent. The gases flowing through the exhaust passage 40 are extremely hot inasmuch as they consist of arcing products or gases that have been heated by the arc. After passing through the exhaust passage 40, these hot gases enter the muffler assembly 9, from which they are discharged to the surrounding atmosphere in a manner which will soon be described in more detail.

Referring now to FIG. 3, an enlarged sectional view along the line 3-3 of FIG. 1 is shown of the exhaust muffler assembly 9. Spaced-apart parallel plates 45 and 46, which are perpendicular to the axis of the exhaust passage 40, are arranged to receive suitable tie bolts extending therethrough, such as shown at 47, to clamp therebetween the respective elements that form the improved exhaust muffler assembly of the present invention. The right-hand plate 45 has a suitable central aperture 48 aligned with the exhaust passage 40 from the pressurized tank 10 of FIG. 2. This central aperture may be thought of as an inlet to the muffler through which the exhaust gases enter the muffler and are directed axially thereof.

Attached to the opposed end wall 46 in alignment with central opening 48 is a generally conical deflector 50, which has its vertex region 51 projecting from the base of the conical deflector toward the opening 48. A centrally located stud 52 is used for attaching deflector 50 to end wall 46. Stud 52 extends through aligned central openings in the deflector and end wall, and nuts on its ends clamp these two parts together. Other suitable means, such as welding, could alternatively be used for attaching the deflector 50 to wall 46.

Surrounding conical deflector 50 is a tubular metal member 56, which is clamped between the end walls 45 and 46. This tubular member 56 contains a large number of perforations 58 extending generally radially thereof at spaced-apart locations about the major portion of the periphery and length of the tubular member. The space 60 enclosed by the tubular member 56 may be thought of as a diffuser chamber. As will soon appear more clearly, exhaust gases flow into the diffuser chamber 60 via inlet 48 and pass radially outwardly from the diffuser chamber via the perforations 58.

Surrounding the difiuser chamber 60 is an annular expansion chamber 62, the inner periphery of which is defined by the first tubular member 56 and the outer periphery of which is defined by a second tubular member 64 mounted in spaced apart concentric relationship to the first tubular member 56. Tubular member 64 contains a large number of radially extending perforations 65, which are confined to end regions thereof adjacent the end walls 45 and 46. The longitudinally central region of tubular member 64 is substantially imperforate.

Compared to the diffuser chamber 60, the expansion chamber 62 has a relatively large volume that allows the exhaust gases entering through holes 58 to expand by a relatively large amount, e.g., from a peak pressure of about 250 p.s.i. in the diffuser chamber to a peak pressure of about 125 p.s.i. in the expansion chamber. These expanded gases flow out of the expansion chamber in a radially outward direction via the above-described perforation 65 at the ends of tubular member 64.

Surrounding the second tubular member 64 in concentric spaced-apart relationship is a third tubular member 70. The space 72 between tubular members 64 and 68 is referred to herein as a reentry chamber. The third tubular member 70 contains a large number of radially extending perforations 74, which are confined to its longitudinally central region. The regions of the tubular member adjacent the end walls 45 and 46 are substantially imperforate. It will thus be seen that the perforations 74 in third tubular member 70 are in a longitudinally staggered location with respect to the perforations 65 in the second tubular member 64. The exhaust gases entering reentry chamber 72 through openings 65 expand further in the reentry chamber, e.g., from 125 p.s.i. to 60 p.s.i. peak pressure, and flow radially outwardly therefrom via the centrally located holes 74 in tubular member 70.

Surrounding the third tube 70 is concentric spaced-apart relationship is a substantially imperforate fourth tubular member 75. The space between the third and fourth tubular members is another expansion chamber, which is filled with a compacted filler 77 of copper wool or a similar substance that retains a porous quality when suitably compacted; This mass of porous material 77 is referred to herein as a random diffuser. The two end walls 45 and 46 contain a large number of openings 78 that are radially aligned with the random diffuser 77 and serve as exhaust openings therefrom. Accordingly, the gases entering the random diffuser through the centrally located holes 74 pass axially of the random diffuser 77 and exit through the exhaust openings 78 at the ends of the diffuser 77. About half of these gases flow to the left through the random diffuser, and about half-flow to the right, as indicated by the arrows 80 and 81. Because the outer tube is substantially imperforate, the exhaust gases cannot flow directly radially across the random filler but are forced to make a turn in the filler and flow axially thereof.

For introducing still another turn into the path of the exhaust gases, a baffle 84 is attached to end wall 46 in spacedapart relationship thereto. This baffle 84 is located in the path of the exhaust gases flowing through exhaust opening 78 and forces these gases to turn radially outward before entering the surrounding atmosphere through an outlet area 82.

It has been found that the tank 10 can act in a manner very similar to that of the baffle 84 inasmuch as the tank wall is positioned in front of the exhaust opening 78 at the right-hand end of the muffler. Accordingly, no separate baffle is used at the right-hand end of the muffler, and the tank wall is relied upon for introducing the extra turn into the path of the exhaust gases and for forcing them to flow radially outward after passing through exhaust openings 78. The outlet area at this end of the muffler between tank 10 and end wall 46 is designated 83.

A main purpose of the diffuser chamber 60 is to break up the large jet that enters the muffler from the circuit breaker via tube 40 into many small jets, which exhaust radially outwardly from the diffuser chamber 60 through the many perforations 58. This transformation from a large jet into many small jets is especially helpful in attenuating and preventing the formation of low-frequency vibrations and also serves, to a lesser extent, to reduce high-frequency vibrations.

The conical deflector 50 helps to distribute gas flow more uniformly among the holes 58 in the tubular wall 56 of diffuser chamber 60. Without this deflector, there is a tendency for the flow to concentrate in the holes at the left-hand end of the muffler; but with the diffuser, this concentration is reduced and the holes at the right-hand end of the diffuser chamber receive a more nearly equal share of the flow. By distributing the flow more uniformly, and total mass flow through wall 56 is greater and the back pressure is maintained at a lower level.

Another function served by the central conical deflector 50 is that it helps prevent a reflected pressure wave from being developed and transmitted back to the circuit interrupter via the gas flowing through tube 40. Such a reflected pressure wave would interfere with the desired flow through the arcing region of the interrupter. Still another function of the deflector is more smoothly and gradually turn the gas flow upon its reaching the outer end of the muffler instead of allowing it to sharply impact against the outer end wall and create a loud drumming action on this end wall.

The expansion chamber 62 serves, among other things, to transiently store a large portion of the gas mass entering the muffler, thus allowing the gas mass to be discharged at a lower rate through the holes 65, 74 downstream therefrom without developing an excessive back pressure upstream from the expansion chamber. It is to be noted that before entering the expansion chamber 62, much of the sound energy, as well as the kinetic and potential energy, in the pressurized gas has been dissipated by virtue of its passage through the small holes 58 in the diffuser chamber wall 56.

In following a path through the reentry chamber 72 from inlet opening 65 through exit opening 74, the exhaust gases are forced to make two substantially 90 turns, as indicated by the arrows 87. These two turns result from the longitudinally staggered relationship of the location of exit holes 74 with respect to the location of the entry hole 65. These turns serve to dissipate both sonic energyand aerodynamic energy and are I especially helpful in attenuating high-frequency vibrations.

The area of the exit holes 74 fromthe reentry chamber 72 is made as small as possible, subject, however, to the limitation that it must be kept large enough to avoid raising the back pressure excessively, By dividing the gas flow into small jets at the exhaust from the reentry chamber, the generation of lowfrequency vibrations at this point is inhibited.

The porous filler material 77, through which the exhaust gases pass after leaving the reentry chamber, serves to further diffuse the gases and to further attenuate flow noises that may have escaped through upstream components of the muffler. The effectiveness of the filler 77 in performing its function is improved bythe fact that the exhaust gases are forced to flow axially through substantially half the length the cylinder formed by the filler instead of being permitted to flow through a short path extending directly radially across the cylinder. The imperforate character of the outer cylinder 75 is responsiblefor directing the exhaust gases in this manner through the filler and is also responsible for introducing an additional 90 turn into the flow path. This additional turn further assists in attenuating high-frequency vibrations.

It was pointed out hereinabove that the baffle 84 at one end of the muffler and the wall of tank at the opposite end force the exhaust gases to make one more turn before entering the surrounding atmosphere, and these additional turns further attenuate high-frequency vibrations.

ltis to be noted that there are no straight line paths leading from the inner chambers of the muffler to exterior that are not intercepted by solid wall potions of the muffler. For example, any straight line paths through the opening 65 of the second cylinder 64 are intercepted by the solid wall of the third cylinder 70, and any solid line paths even through the exhaust openings 74 in the reentry chamber are intercepted by the outer cylinder 75. These solid walls serve as barriers for inhibiting the radiation of sound energy into the surrounding atmosphere. For assisting the walls in performing this function, each of the solid wall portions, wherever practical, is coated with a suitable vibration damping material, such as the filled epoxy material available from Soundcoat Company, Incorporated, under the name Epoxy-10 damping compound. This material reduces the ring and vibration of the wall when it is struck by the gas flow and accompanying shock wave as well as reducing the transfer of sound energy through the wall.

It is to be further noted that most of the noise entering the muffler or generated therein can reach a point remote from the muffler only after having passed through two solid wall portion or through the tortuous path represented by the arrows leading through the muffler from the diffuser chamber 60 to its outside. The many turns and the many small orifices in the tortuous path effectively attenuate he sound energy transmitted along this path, as was pointed out hereinabove. As for the double solid wall barrier, note that the outer two cylinders 70 and 75 present a double solid wall barrier in any straight line path leading radially outward through openings 65 in the expansion chamber. It will be apparent that the axially offset or staggered location of the next group of holes 74 with respect to holes 65 contributes importantly to the availability of this double solid wall. As for those straight line paths extending axially of the muffler to the left in FIG. 3, the end wall 46 and barrier 84 constitute a double solid wall barrierin most such paths. The other end wall and the wall of tank 10 constitute a double solid wall barrier in most straight line paths extending axially of the muffler to the right in FIG. 3. The vibration damping material 90 on most of the solid walls of the double-wall barriers increase their efiectiveness in attenuating sound transmission. Only those few diagonally extending straight line paths extending through the end walls 45 and 46 and outlet areas 82 and 83 are intercepted by less than two solid walls.

. The previously referred to operating mechanism of the circuit breaker, which is disposed inside the hollowv casing 20 within the tank 10, is a pneumatically operated mechanism from which pressurizedair must be dumped to initiate its operation.,This dumping occurs just prior to opening of the blast valve 38 that initiates the aroextinguishing blast through tube 40 into the muffler. Through the amount of air vented from the mechanism is relatively small compared to that used for the arc-extinguishing blast, objectionable noises can still be created by dumping this air directly into the surrounding atmosphere. For reducing the noises produced by the flow of such air, we exhaust this air into the expansion chamber 62 of our muffler 9 via a line 95 passing through end plate 45. The expansion chamber, in view of its large volume, is able to receive this air without an appreciable rise in pressure, thus producing no appreciable effect on the above-described operation of the muffler. An advantage of exhausting into the expansion chamber 62 instead of the diffuser chamber 60 is that during muffler operation the pressure in the expansion chamber is muchless than that in the diffuser chamber and changes less rapidly, thus resulting in less chance of a shock wave being reflected back through the line 95 to the operating mechanism. A severe shock wave could interfere with proper operation of the mechanism.

The above-described muffler, through considerably less expensive than the-muffler shown in the aforesaid U.S. Pat. No.

3,l34,876,has demonstrated that it can appreciably reduce the noise emitted from the circuit breaker. More specifically, with the present muffler we have been able to hold the noise level to about 104 db. at 35 feet as compared to about I20 db. for the muffler of the patent under the same interrupting conditions. Thcpresent muffler also limits the back pressure sufficientlyas not to interfere with interruption or the ability of the breaker to rapidly reclose and reopen.

Further improvements in noise-reducing ability can be achieved bypreserving the random flow pattern of the gas passing through the random diffuser 77 as it leaves the diffuser. This can be accomplished by using the most open possible screening or the like for retaining the diffuser material at the outer ends of the muffler. Such screening is schematically shown in FIG. 4 at 95. The exiting gases can pass through this screening without recombining into jets. Where used, this screening would replace the perforated outer peripheral region of the end plates 45 and 46.

While we have shown and described particular embodi ments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broader aspects; and we, therefore, intend herein to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desired to secure by Letters Patent of the United States is:

I. In a gas-blast circuit breaker having an exhaust passage through which pressurized gases are exhausted after flowing through the arcing region of the circuit breaker, a noise reducing exhaust muffler comprising:

a. a pair of spaced-apart end walls and a first tubular member extending axially of the muffler between said end walls to define a diffuser chamber internally thereof,

. said first tubular member having perforations extending generally radially therethrough at spaced-apart locations about a major portion of the periphery and length of said tubular member for allowing exhaust gases to flow generally radially outward therethrough,

c. an inlet to the diffuser chamber in one of said end walls adapted to communicate with said exhaust passage for directing exhaust gases axially of the muffler toward said other end wall,

. a generally conical deflector on said other end wall having a base surrounded by said first tubular member and having a vertex region projecting from said base toward said one end wall,

a second tubular member surrounding and radially spaced from said first tubular member and defining the outer perimeter of an expansion chamber between said first and second tubular members,

. a third tubular member surrounding and radially spaced from said second tubular member and defining the outer periphery of a reentry chamber between said second and third tubular members,

. said second and third tubular members each having perforations extending generally radially therethrough,

h. said second tubular member having far more perforations in its end regions than in its longitudinally central region,

. said third tubular member having far more perforations in its longitudinally central region than in its regions adjacent said end walls,

. a fourth tubular member surrounding and radially spaced from said third tubular member and defining the outer perimeter of another expansion chamber between said third and fourth tubular members,

. and a quantity of compacted porous material disposed in the space between said third and fourth tubular members.

2. The structure of claim 1 in which said second tubular member is substantially imperforate in its longitudinally central region spaced from said end walls and said third tubular member is substantially imperforate in its regions adjacent said end walls.

3. The structure of claim 1 in which said fourth tubular member is substantially imperforate but said muffler contains exhaust openings at its opposite end aligned with the space between said third and fourth tubular members to allow exhaust gases to be vented from said muffler after passing axially of said muffler through said compacted porous material.

4. The structure of claim 1 in which:

a. said second tubular member is substantially imperforate in its longitudinally central region but has many perforations in its regions adjacent said end walls,

b. said third tubular member is substantially imperforate in its regions adjacent said end walls but has many perforations in its longitudinally central region, c. the location of the perforations in said third tubular member being longitudinally staggered with respect to the locations of the perforations in said second tubular member so that gases flowing through said reentry chamber are forced to make two approximately 90 turns in said reentry chamber.

5. The structure of claim 3 in which a baffle is provided adjacent said other end wall but spaced therefrom, said baffle being disposed in the path of gases flowing through said exhaust openings at said other end of the muffler to force said exhaust gases to make another turn before entering the surrounding atmosphere.

6. In a circuit breaker constructed as in claim 1 and further comprising a tank adjacent which said one end wall of said muffler is mounted in spaced relationship, the wall of tank acting as a baffle which forces exhaust gases flowing through the exhaust openings at said one end of the muffler to make another turn before entering the surrounding atmosphere.

7. In a circuit breaker constructed as in claim 3, a baffle provided adjacent said other end wall of the muffler but spaced therefrom, said baffle being disposed in the path of gases flowing through said exhaust openings at said other end of the muffler to force said exhaust gases to make another turn before entering the surrounding atmosphere, a tank adjacent which said one end wall of the muffler is mounted in spaced relationship, the wall of said tank acting as a baffle which forces exhaust gases flowing through the exhaust openings at said one end of the muffler to make another turn before entering surrounding atmosphere.

3. The circuit breaker of claim 1 in which said muffler is so constructed that a double solid wall barrier intersects substantially all straight line paths extending from said expansion chamber to the surrounding atmosphere.

9. The circuit breaker of claim 1 in which most of the solid wall portions of said muffler are coated with a vibration damping material.

10. In a circuit breaker constructed as in claim 1 and further comprising a pneumatic-operating mechanism from which pressurized gas is exhausted during the early stages of circuit breaker operation, a passageway through which said pressurized gas is exhausted from said mechanism, said passageway having an outlet through which gases can flow directly into said expansion chamber without passing through said diffuser chamber.

11. The structure of claim 3 in which said exhaust openings are defined by structure with large open areas that allow said exhaust gases to pass therethrough from said porous material without recombining into jets. 

1. In a gas-blast circuit breaker having an exhaust passage through which pressurized gases are exhausted after flowing through the arcing region of the circuit breaker, a noisereducing exhaust muffler comprising: a. a pair of spaced-apart end walls and a first tubular member extending axially of the muffler between said end walls to define a diffuser chamber internally thereof, b. said first tubular member having perforations extending generally radially therethrough at spaced-apart locations about a major portion of the periphery and length of said tubular member for allowing exhaust gases to flow generally radially outward therethrough, c. an inlet to the diffuser chamber in one of said end walls adapted to communicate with said exhaust passage for directing exhaust gases axially of the muffler toward said other end wall, d. a generally conical deflector on said other end wall having a base surrounded by said first tubular member and having a vertex region projecting from said base toward said one end wall, e. a second tubular member surrounding and radially spaced from said first tubular member and defining the outer perimeter of an expansion chamber between said first and second tubular members, f. a third tUbular member surrounding and radially spaced from said second tubular member and defining the outer periphery of a reentry chamber between said second and third tubular members, g. said second and third tubular members each having perforations extending generally radially therethrough, h. said second tubular member having far more perforations in its end regions than in its longitudinally central region, i. said third tubular member having far more perforations in its longitudinally central region than in its regions adjacent said end walls, j. a fourth tubular member surrounding and radially spaced from said third tubular member and defining the outer perimeter of another expansion chamber between said third and fourth tubular members, k. and a quantity of compacted porous material disposed in the space between said third and fourth tubular members.
 2. The structure of claim 1 in which said second tubular member is substantially imperforate in its longitudinally central region spaced from said end walls and said third tubular member is substantially imperforate in its regions adjacent said end walls.
 3. The structure of claim 1 in which said fourth tubular member is substantially imperforate but said muffler contains exhaust openings at its opposite end aligned with the space between said third and fourth tubular members to allow exhaust gases to be vented from said muffler after passing axially of said muffler through said compacted porous material.
 4. The structure of claim 1 in which: a. said second tubular member is substantially imperforate in its longitudinally central region but has many perforations in its regions adjacent said end walls, b. said third tubular member is substantially imperforate in its regions adjacent said end walls but has many perforations in its longitudinally central region, c. the location of the perforations in said third tubular member being longitudinally staggered with respect to the locations of the perforations in said second tubular member so that gases flowing through said reentry chamber are forced to make two approximately 90* turns in said reentry chamber.
 5. The structure of claim 3 in which a baffle is provided adjacent said other end wall but spaced therefrom, said baffle being disposed in the path of gases flowing through said exhaust openings at said other end of the muffler to force said exhaust gases to make another turn before entering the surrounding atmosphere.
 6. In a circuit breaker constructed as in claim 1 and further comprising a tank adjacent which said one end wall of said muffler is mounted in spaced relationship, the wall of tank acting as a baffle which forces exhaust gases flowing through the exhaust openings at said one end of the muffler to make another turn before entering the surrounding atmosphere.
 7. In a circuit breaker constructed as in claim 3, a baffle provided adjacent said other end wall of the muffler but spaced therefrom, said baffle being disposed in the path of gases flowing through said exhaust openings at said other end of the muffler to force said exhaust gases to make another turn before entering the surrounding atmosphere, a tank adjacent which said one end wall of the muffler is mounted in spaced relationship, the wall of said tank acting as a baffle which forces exhaust gases flowing through the exhaust openings at said one end of the muffler to make another turn before entering surrounding atmosphere.
 8. The circuit breaker of claim 1 in which said muffler is so constructed that a double solid wall barrier intersects substantially all straight line paths extending from said expansion chamber to the surrounding atmosphere.
 9. The circuit breaker of claim 1 in which most of the solid wall portions of said muffler are coated with a vibration damping material.
 10. In a circuit breaker constructed as in claim 1 and further comprising a pneumatic-operating mechanism from which pressurized gas is exhausted during the Early stages of circuit breaker operation, a passageway through which said pressurized gas is exhausted from said mechanism, said passageway having an outlet through which gases can flow directly into said expansion chamber without passing through said diffuser chamber.
 11. The structure of claim 3 in which said exhaust openings are defined by structure with large open areas that allow said exhaust gases to pass therethrough from said porous material without recombining into jets. 